Evaluation of heart rate variability in pediatric patients with beta thalassemia major: Cross-sectional study

Figure 2 Heart rate variability analysis in a healthy control. A: Spectral and time-domain plots of heart rate variability (HRV) in a 7-year-old healthy control child over 24 hours, including awake and sleep phases. HRV parameters are within normal limits for age [e.g., standard deviation of all normal-to-normal intervals (SDNN): 124, root mean square of successive differences: 57], with clear circadian variation (e.g., SDNN 118 awake vs 108 asleep), showing balanced sympathetic and parasympathetic modulation with appropriate circadian variation; B: Corresponding 24-hour HRV spectral power distribution and RR interval histogram from the same child, demonstrating high total power (3155.0 ms²) with balanced low-frequency (608.3) and high-frequency (470.0) components, consistent with intact autonomic regulation. VLF: Very low frequency; LF: Low frequency; HF: High frequency; SDNN: Standard deviation of all normal-to-normal intervals; SDANN: Standard deviation of the 5-minutes average normal-to-normal intervals; RMSSD: Root mean square of successive differences; pNN50: Percentage of successive normal-to-normal intervals differing by > 50 ms.